135 lines
4 KiB
Go
135 lines
4 KiB
Go
// Copyright (c) 2013 Conformal Systems LLC.
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// Use of this source code is governed by an ISC
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// license that can be found in the LICENSE file.
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package btcwire
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import (
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"fmt"
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"io"
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)
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// MsgGetHeaders implements the Message interface and represents a bitcoin
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// getheaders message. It is used to request a list of block headers for
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// blocks starting after the last known hash in the slice of block locator
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// hashes. The list is returned via a headers message (MsgHeaders) and is
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// limited by a specific hash to stop at or the maximum number of block headers
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// per message, which is currently 2000.
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//
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// Set the HashStop field to the hash at which to stop and use
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// AddBlockLocatorHash to build up the list of block locator hashes.
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//
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// The algorithm for building the block locator hashes should be to add the
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// hashes in reverse order until you reach the genesis block. In order to keep
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// the list of locator hashes to a resonable number of entries, first add the
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// most recent 10 block hashes, then double the step each loop iteration to
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// exponentially decrease the number of hashes the further away from head and
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// closer to the genesis block you get.
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type MsgGetHeaders struct {
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ProtocolVersion uint32
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BlockLocatorHashes []*ShaHash
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HashStop ShaHash
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}
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// AddBlockLocatorHash adds a new block locator hash to the message.
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func (msg *MsgGetHeaders) AddBlockLocatorHash(hash *ShaHash) error {
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if len(msg.BlockLocatorHashes)+1 > MaxBlockLocatorsPerMsg {
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str := "MsgGetHeaders.AddBlockLocatorHash: too many block " +
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"locator hashes for message [max %v]"
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return fmt.Errorf(str, MaxBlockLocatorsPerMsg)
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}
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msg.BlockLocatorHashes = append(msg.BlockLocatorHashes, hash)
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return nil
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}
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// BtcDecode decodes r using the bitcoin protocol encoding into the receiver.
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// This is part of the Message interface implementation.
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func (msg *MsgGetHeaders) BtcDecode(r io.Reader, pver uint32) error {
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err := readElement(r, &msg.ProtocolVersion)
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if err != nil {
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return err
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}
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// Read num block locator hashes and limit to max.
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count, err := readVarInt(r, pver)
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if err != nil {
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return err
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}
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if count > MaxBlockLocatorsPerMsg {
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str := "%v: too many block locator hashes in message [%v]"
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return fmt.Errorf(str, "MsgGetHeaders.BtcDecode", count)
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}
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for i := uint64(0); i < count; i++ {
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sha := ShaHash{}
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err := readElement(r, &sha)
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if err != nil {
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return err
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}
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msg.AddBlockLocatorHash(&sha)
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}
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err = readElement(r, &msg.HashStop)
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if err != nil {
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return err
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}
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return nil
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}
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// BtcEncode encodes the receiver to w using the bitcoin protocol encoding.
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// This is part of the Message interface implementation.
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func (msg *MsgGetHeaders) BtcEncode(w io.Writer, pver uint32) error {
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// Limit to max block locator hashes per message.
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count := len(msg.BlockLocatorHashes)
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if count > MaxBlockLocatorsPerMsg {
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str := "MsgGetHeaders.BtcEncode: too many block locator " +
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"hashes in message [%v]"
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return fmt.Errorf(str, count)
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}
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err := writeElement(w, msg.ProtocolVersion)
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if err != nil {
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return err
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}
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err = writeVarInt(w, pver, uint64(count))
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if err != nil {
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return err
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}
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for _, sha := range msg.BlockLocatorHashes {
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err := writeElement(w, sha)
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if err != nil {
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return err
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}
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}
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err = writeElement(w, msg.HashStop)
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if err != nil {
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return err
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}
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return nil
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}
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// Command returns the protocol command string for the message. This is part
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// of the Message interface implementation.
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func (msg *MsgGetHeaders) Command() string {
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return cmdGetHeaders
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}
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// MaxPayloadLength returns the maximum length the payload can be for the
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// receiver. This is part of the Message interface implementation.
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func (msg *MsgGetHeaders) MaxPayloadLength(pver uint32) uint32 {
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// Version 4 bytes + num block locator hashes (varInt) + max allowed block
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// locators + hash stop.
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return 4 + maxVarIntPayload + (MaxBlockLocatorsPerMsg * HashSize) + HashSize
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}
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// NewMsgGetHeaders returns a new bitcoin getheaders message that conforms to
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// the Message interface. See MsgGetHeaders for details.
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func NewMsgGetHeaders() *MsgGetHeaders {
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return &MsgGetHeaders{}
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}
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